1. Field of the Invention
This invention relates to a pump, valve and electronic system and a process which will deliver a liquid solvent mixture at elevated pressures for liquid chromatography and similar applications. More particularly, it relates to such a system and process which will vary the proportions of the solvent mixture components and solvent flow rate smoothly at pressures of up to about 6,000 psi.
2. Description of the Prior Art
A variety of solvent delivery systems for supplying solvent mixtures for liquid chromatography and related applications are known in the art. Two basic approaches are employed in the art, both using two pistons. The first approach uses one piston to deliver liquid to the column while the second piston is used to refill the solvents from liquid containers. A sudden reversal of one piston injects solvent solution from a low pressure cylinder into a high pressure cylinder. The second approach uses the two pistons in such a way that at least one piston is always dispensing liquid to the chromatographic column. One piston is used for a part of the pump cycle to refill solvents from the liquid containers and for another part of the pump cycle to dispense liquid into the column and to refill the second piston. While the first piston is refilling the second piston is dispensing liquid to the column. A drawback of' the first approach is that the injection step produces undesirable pressure pulsing in the system, necessitating the use of a pulse damping reservoir. Such a reservoir increases system volume, and a low system volume is desired for rapid solvent composition changes. A drawback of the second approach is that it requires a mixer in addition to the two reverse pistons, which also increases system volume and contributes to system complexity.
Examples of prior art solvent delivery systems are disclosed in the following issued U.S. patents: U.S. Pat. Nos. 4,137,011, issued Jan. 30, 1979 to Rock; 4,173,437, issued Nov. 6, 1979 to Leka et al. and 4,260,342, issued April 7, 1981 to Leka et al. Another example of a prior art solvent delivery system is described in commonly assigned pending application Ser. No. 561,219, filed Dec. 14, 1983, by Keith S. Clark, entitled "Solvent Proportioning and Mixing Apparatus and System". A further indication of the state of the art is contained in the following references: Savage, M., "Accuracy and Reproducibility in a Two-Pump Gradient HPLC", American Laboratory, May 1979, pp. 49-57; Conlon, R. D. et al., "An Advanced LC System", American Laboratory, Sept. 1982; Schwartz, H. et al., "A Dual Syringe LC Solvent Delivery System for Use with Microbore Columns", American Laboratory, October 1984, pp. 43-58; Fielding, R. M., "A Low-Cost Automated Step-Gradient HPLC System", LC, Vol. 2, No. 7, pp. 532-535. Commercially available solvent delivery systems are available under the following designations: "Spectroflow 430" from Kratos Analytical Instruments, Ramsey, N.J. "miniPump VS" from LDC/Milton Roy, Riviera Beach, Fla.; "Varian Model 5560" from Varian Associates, Palo Alto, Calif.; "SP 8700" from Spectra-Physics, Mountain View, Calif.; "Waters Model 510" from Millipore; "HP 1090" from Hewlett Packard, Palo Alto, Calif.; "Model 112" from Beckman Instruments, Fullerton, Calif.; and "Series 4LC" from Perkin-Elmer Corp., Norwalk, Conn.
Due to system complexity necessary to achieve high performance, the high performance systems in the above examples, such as the Perkin-Elmer Model 4LC, are quite expensive. While the art of these solvent delivery systems is a highly sophisticated one, there is a substantial need to achieve such high performance at a significantly reduced cost.